No deco time proximity.

[dmaziuk]

Let's say that two divers on an NDL dive have the same careful ascent followed by a solid safety stop and have reached the point that they are safe to go to the surface. Diver A goes to the surface, and Diver B stays in the water for an extra 5 minutes.

When Diver B gets out of the water, yes, he will have less nitrogen in his body when he exits the water than Diver A had when he exited the water. But it's 5 minutes later now, and Diver A has been off-gassing faster while on the surface. So, at that point in time, Diver A has less nitrogen in his system than Diver B does. If they do a second dive together, Diver A will have less residual nitrogen at the start of the dive than Diver B.

The bubble argument is that if bubbles get too large to pass through the walls of alveoli, they have to be re-absorbed before they can be eliminated. That takes time. By that argument Diver A may have more nitrogen in their system than Diver B 5 minutes later. They may get even 6 minutes later, or 20, who knows. Ken's table suggests it's more than 12 minutes.

Personally when I've spent my 5 minutes at SS depth and have a choice to go up and do a surface swim, or stay down and follow the sand to shore, I choose the latter.

 

[dmaziuk]

Let's look once again at what I said and what others have said.

This:

As was asked and no yet answered, this sort of super slow and conservative ascent would seem to be a pretty significant disadvantage. When everyone else is topside, warm and dry, relaxing and OFF GASSING fast, he is off gassing very slowly if not actually on gassing slow tissue.

This would seem to make the second dive a lot shorter or more aggressive with respect to decompression stress.

A extra slow ascent on the last dive of the day is different than one that proceeds a repetitive dive.

I don't argue that the profile that was posted is "super slow" and likely suboptimal. I argue that equating "off gassing fast" to "less decompression stress" is, at best, overly simplistic. To the point of being likely untrue in a number of cases.

 

[boulderjohn]

To the point of being likely untrue in a number of cases.

specifically....

 

[johndiver999]

This:



I don't argue that the profile that was posted is "super slow" and likely suboptimal. I argue that equating "off gassing fast" to "less decompression stress" is, at best, overly simplistic. To the point of being likely untrue in a number of cases.

The comments about the super slow ascent protocol - which for most people is probably overkill is that it MIGHT impact the NDL on SUBSEQUENT dives. The whole point of this little side bar discussion, is that a super slow ascent might limit your second dive or put you closer to the No deco limit for a second dive. Especially if your surface interval was less than maybe an hour or so.

I assume a dive computer would account for the super slow ascent and relatively shorter surface interval. Perhaps decompression stress is a poor word choice and a more correct one would simply be residual nitrogen, since that is what we are trying to discuss. I think I started using that term and it might be partly to blame for some confusion.

If a diver were on a recreational boat where the group's maximum surface interval scheduled was 50 minutes and a diver spends 15 minutes of the allotted surface interval time underwater, I can see how that could have consequences.

 

[dmaziuk]

If a diver were on a recreational boat where the group's maximum surface interval scheduled was 50 minutes and a diver spends 15 minutes of the allotted surface interval time underwater, I can see how that could have consequences.

Obviously if a diver spends those 15 minutes at one hundred feet down, that can't be good, but I think we all get it already that spending more time at deep stop and less time topside does not magically shorten decompression times.

The point of the argument is that if you split your hour SI to 15 minutes @ SS + 45 minutes topside, you'll surface with lower bubble score than the guy doing 3 minutes SS + 57 minutes SI. The guy with more bubbles may also eliminate less nitrogen by the end of that hour, if you believe the "worse diffusion" theory.

 

[EireDiver606]

You never ascend just because your computer tells you. You should understand deco theory, and use the computer as a tool, not be dependent on it.

You use your head to dive, not a computer. But a computer can definitely be beneficial as long as you’re not dependent on it.

It’s the same as saying, you use a razor to shave, not a mirror. The mirror definitely helps you shave the same as a dive computer.

 

[boulderjohn]

You never ascend just because your computer tells you. You should understand deco theory, and use the computer as a tool, not be dependent on it.

You use your head to dive, not a computer. But a computer can definitely be beneficial as long as you’re not dependent on it.

I'm glad you decided to stop giving opinions about topics you don't know about.

So are now an expert on decompression theory. What would you say is the correct way to know when to ascend if you aren't going to pay attention to your computer? How do you "use your head" to ascend? Are you following this older GUE statement on why people should not use computers?

 

[EireDiver606]

I'm glad you decided to stop giving opinions about topics you don't know about.

So are now an expert on decompression theory. What would you say is the correct way to know when to ascend if you aren't going to pay attention to your computer? How do you "use your head" to ascend? Are you following this older GUE statement on why people should not use computers?

Definitely not an expert on anything, nor do I act like it. Far far from it mate not sure why you’re picking a bone with me just because I said it’s good not to be dependent on computers.

 

[boulderjohn]

Definitely not an expert on anything, nor do I act like it. Far far from it mate not sure why you’re picking a bone with me just because I said it’s good not to be dependent on computers.

What I am picking a bone with is your making statements telling people what to do when I don't know what you mean by it--and I suspect you don't know what it means, either.

Can you tell me what you should do on a decompression dive so that you are not dependent upon a computer? How would you dive instead?

 

[EireDiver606]

What I am picking a bone with is your making statements telling people what to do when I don't know what you mean by it--and I suspect you don't know what it means, either.

Can you tell me what you should do on a decompression dive so that you are not dependent upon a computer? How would you dive instead?

?

I never told anyone what to do and why would I? They can dive how they want. Deco theory doesn’t have to be complicated technical stuff, my understanding is that it can be what time you have at x depth, breathing x gas and if you go past that, how much deco you have.